Cleaning sheet and method for a probe

ABSTRACT

A cleaning sheet has a base sheet, a foamed layer of a porous material on the base sheet and a polishing layer formed on the foamed layer. The foamed layer includes non-fibrous abrading particles and air bubbles. Such a cleaning sheet may be produced by preparing a paint having air bubbles dispersed inside by mechanically foaming a foaming material containing a foaming resin material and abrading particles, forming on the base sheet a foamed layer having abrading particles dispersed inside by coating a surface of the base sheet with this paint and drying it, and forming a polishing layer on the foamed layer. A probe having a tip may be cleaned with such a cleaning sheet by causing a surface of its polishing layer to be pressed against the tip of the probe and causing the tip of the probe to penetrate the polishing layer and further to be inserted into the foamed layer having abrading particles dispersed inside.

This is a continuation-in-part of application Ser. No. 10/298,310 filedNov. 14, 2002, now pending.

BACKGROUND OF THE INVENTION

This invention relates to a cleaning sheet for and a method of removingforeign substances attached to the tip and side surfaces of a probe usedfor inspecting a planar target object such as a semiconductor devicehaving integrated circuits installed thereon.

Chips are produced by installing semiconductor elements and integratedcircuits on a semiconductor wafer through various wafer-producingprocesses. The chips thus produced on a semiconductor wafer are cut offfrom the wafer after a current-passing test and are packaged. Tests witha current are carried out also before and after the packaging toseparate faulty products stringently from qualified products.

Such current-passing tests are carried out by means of a test apparatusof a known kind such as a wafer prober. A position-matching process bymoving a prober needle (“probe”) serving as an electrode of a tester andthe electrodes on the chip (pads or lead lines) and a contacting processbetween the probe and the chip electrodes are repeated for carrying outelectrical measurements of different kinds.

While such position-matching and contacting processes are repeated bymoving the probe and the electrodes on the chips, the tip of the probeslides over the electrodes on the chips, scraping off portions of theelectrodes. Such portions of the electrodes that have been scraped offbecome attached to the tip and the side surfaces of the probe as foreignsubstances.

The foreign substances, that thus become attached to the probe, aremetals such as aluminum. If such a metal is oxidized, the electricalcontact resistance between the probe and the electrodes on the chipbecomes larger, making it impossible to carry out accurate electricalmeasurements. Thus, it is necessary to clean the tip portion of theprobe regularly after each time a specified number of contact processeshave been carried out in order to remove such foreign substances fromthe probe.

Removal of such foreign substances from the tip portion of a probe iscarried out by using the same apparatus used for the current-passingtests such as the aforementioned wafer prober, except the target objectto be tested such as a semiconductor wafer attached to the apparatus isreplaced with a cleaning device having a similar shape. Examples of aprior art cleaning device of this kind include hard polishing plates ofa grinding stone, glass and a ceramic material (as disclosed, forexample, in Japanese Patent Publications Tokkai 7-199141, 5-209896,5-166893, 4-96342 and 3-105940) and sheets with a polishing layer formedon an uneven surface of an elastic member having protrusions andindentations (as disclosed, for example, in Japanese Patent PublicationTokkai 2000-332069). The probe is pressed against the surface of such acleaning device, as done in the aforementioned current-passing test.

If a polishing plate of a hard material is used as the cleaning deviceand the probe is pressed too hard against it, its tip portion willbecome deformed and hence it is necessary to reduce the pressure withwhich the probe can be pressed against the cleaning device. As a result,only the portions very close to the tip can be cleaned. If a cleaningdevice of the type with a polishing layer formed on an elastic member isused, on the other hand, the tip of the probe penetrates the polishinglayer and cannot be cleaned sufficiently. Thus, the common practice hasbeen to provide separately a device for cleaning the tip and anotherdevice for cleaning the side surfaces, attaching them to acurrent-passing test apparatus consecutively one at a time. It wastherefore both cumbersome and time-consuming to clean a probe.

SUMMARY OF THE INVENTION

It is therefore an object of this invention in view of the above toprovide a cleaning sheet capable of cleaning both the tip and the sidesurfaces of a probe, a method of producing such a sheet and also amethod of cleaning a probe.

A cleaning sheet embodying this invention, with which the above andother objects can be accomplished, may be characterized as comprising abase sheet, a foamed layer of a porous material which is formed on thebase sheet and includes non-fibrous abrading particles and air bubbles,and a polishing layer formed on the foamed layer.

Such a cleaning sheet may be produced by preparing a paint having airbubbles dispersed therein by mechanically foaming a foaming materialcomprising a foaming resin material and abrading particles, forming on abase sheet a foamed layer having abrading particles dispersed inside bycoating a surface of the base sheet with this paint and drying it, andforming a polishing layer on a surface of the foamed layer.

Such paint may be produced by sending air into the foaming materialwhile stirring the foaming material and thereby dispersing the airbubbles and the abrading particles inside the paint. Because it is by amechanical means that the foaming material is caused to be foamed, theabrading particles and the air bubbles can be dispersed uniformedthroughout the interior of the foamed layer without strictly maintainingthe conditions for the foaming reaction such as the reaction time andtemperature.

A probe having a tip may be cleaned with a cleaning sheet embodying thisinvention, structured and produced as described above, by causing asurface of its polishing layer to be pressed against the tip of theprobe and thereby causing the tip of the probe to penetrate thepolishing layer and further to be inserted into the foamed layer havingabrading particles dispersed inside. As the tip penetrates the polishinglayer and becomes inserted into the foamed layer having abradingparticles dispersed inside, both the tip and the side surfaces of theprobe become cleaned not only by the abrading particles inside thepolishing layer but also those in the foamed layer.

In summary, with a cleaning sheet thus structured and/or produced, thetip and the side surfaces of a probe can be effectively andsimultaneously cleaned.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a cleaning sheet embodying this inventionwhen a tip portion of a probe is being cleaned therewith.

FIG. 2 is a schematic side view of a wafer prober.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 2 shows a wafer prober 20 of a known kind. When a cleaning processaccording to this invention is effected, a cleaning sheet 10 embodyingthis invention to be described below and shown in FIG. 1 is attached tosuch a wafer prober 20 instead of a target object to be inspected suchas a semiconductor wafer which is normally attached thereto. As shown inFIG. 1, the cleaning sheet 10 is comprised of a base sheet 11, a foamedlayer 12 formed on a surface of the base sheet 11 and a polishing layer13 formed on the surface of the foamed layer 12. The foamed layer 12 isa layer of a porous foamed material containing non-fibrous abradingparticles 14 and many air bubbles inside. Such a cleaning sheet may beproduced by first preparing a paint material by mechanically foaming amaterial including a foaming resin and abrading particle. A surface ofthe base sheet 11 is then coated with this paint material and it isdried so as to form the foamed layer 12 with the abrading particlesdispersed therein. The polishing layer 13 is thereafter formed on thesurface of this foamed layer 12.

The foaming material to be used in the production method described abovemay be obtained by mixing a foaming agent such as a salt of fatty acid,an acrylic thickener, a fluorine or silicon type stabilizer, and alsopowder of aluminum hydroxide with average diameter of 0.01-70 μm forimproving the stabilization effect, and further by mixing in an epoxycross linking agent. As the abrading particles 14, particles of aluminumoxide, silicon carbide, chromium oxide, iron oxide, diamond, boroncarbide, cerium oxide or silicon oxide with average diameter of 0.01-70μm are also mixed into the foaming material in an amount of 5-80 weight%. Throughout herein, the expression “particles” is intended to beinterpreted in a narrow sense of the word, excluding any small objectsthat may be referred to as being fibrous or a fiber particle.

The mechanical foaming of the foaming material thus prepared is effectedwith stirring while sending in air at a specified rate into the foamingmaterial containing the abrading particles 14. As a result of thisprocess, the abrading particles 14 and the air bubbles 15 becomeuniformly dispersed inside the foaming material and a paint with a highdegree of viscosity containing air bubbles is obtained. The foamingmultiplicity of the paint is in the range of 2-5 times. Such amechanical foaming process may be carried out by using a continuoushigh-pressure foaming apparatus (such as TW-70 produced by AikoshaSeisakusho of Japan) used for the continuous mixing process of rawcream.

The paint material with air bubbles may be applied on a surface of thebase sheet 11 by a known method and with a known means such as the knifecoater method and the so-called direct coating method. A sheet with aflat surface of a plastic material such as polyester and polyethyleneterephthalate (PET) may be used as the base sheet 11. The drying processfor the paint applied on the base sheet 11 may be effected in anenvironment with temperature in the range of 90° C. -160° C. In order tocompletely solidify the paint, a far infrared ray may be appliedadditionally. For forming a stable foamed layer 12 with abradingparticles dispersed on the surface of the base sheet 11, furthermore, aventilating means such as a fan may be used to cool it after the foamingpaint coated on the surface of the base sheet 11 is completely dried.After such a drying process, a foamed layer 12 with air bubbles 15 andabrading particles 14 uniformly dispersed throughout is formed on thesurface of the base sheet 11. The thickness of the foamed layer 12 thusproduced is within the range of 50 μm-200 μm.

Since the foamed layer 12 according to this invention is formed by amechanical foaming process rather than by a chemical method, theabrading particles and air bubbles can be uniformly dispersed withoutthe necessity of strictly controlling and maintaining the conditions forthe foaming reaction such as the reaction time and the temperature.

The polishing layer 13 may be formed by preparing a polisher painthaving abrading particles dispersed within a resin solution obtained bydissolving a resin binder selected from polyesters and urethanes in asolvent such as methylethyl ketone, applying it on the surface of thefoamed layer 12 by a known method such as the reverse coating method andthen drying it. The thickness of the polishing layer 13 is in the rangeof 5 μm-30 μm. Particles of silicon carbide, silica, aluminum oxide anddiamond with average diameter of 0.001 μm-10 μm may be used as theabrading particles.

A wafer prober such as shown at 20 in FIG. 2, commonly used forcurrent-passing tests, may be used for cleaning a probe for inspecting aplanar object such as a semiconductor device with integrated circuitsinstalled thereon. As shown in FIG. 2, the wafer prober 20 has a table23 on which a target object for inspection such as a semiconductordevice is intended to be attached. After such a target object forinspection is attached, the table 23 is moved horizontally andvertically for positioning and the target object is pressed against aprobe 22 of a probe card 21 in order to carry out electricalmeasurements of different kinds on the target object. When the probe 22is to be cleaned, the cleaning sheet 10 as described above is attachedto the table 23, instead of the target object for inspection and thetable 23 is similarly moved similarly to press the probe 22 against thesurface of the cleaning sheet 10 attached to the table 23.

The cleaning sheet 10 may be cut into a circular, quadrangular or anyother shape and pasted on the table 23 by means of a double-sideadhesive sheet. Alternatively the cleaning sheet 10 may be pasted on aflat plate of an appropriate shape and this plate may then be attachedto the table 23. In summary, the manner of attaching the cleaning sheet10 onto the table 23 does not limit the scope of the invention.

When the tip of the probe 22 is pressed against the surface of thecleaning sheet 10, it penetrates the polishing layer 13 as shown in FIG.1 and is inserted inside the foamed layer 12 with abrading particles.Both the tip and side surfaces of the probe 22 are cleaned by theabrading particles in the polishing layer 13 as the probe 22 penetratesthe polishing layer 13 and thereafter by the abrading particles 14dispersed in the foamed layer 12. In summary, since both the tip andside surfaces of the probe 22 are also cleaned by the foamed layer 12,those of the foreign materials not removed as the probe penetrates thepolishing layer 13 may be expected to be dependably removed inside thefoamed layer 12 from the tip and the side surfaces of the probe 22.

As a test, a cleaning sheet embodying this invention was produced byadding 2.9 kg of particles of aluminum hydroxide (HM-43 by tradenameproduced by Dai-Nippon Inki Kagaku Kogyo Corporation) for improving thestabilization effect and 2.9 kg of particles of aluminum oxide (WA8000by tradename produced by Fujimi Incorporated) to 28 kg of foamingurethane resin (DICFORM F-505EL by tradename produced by Dai-Nippon InkiKagaku Kogyo Corporation), mixing them together in a pot mill for 96hours and thereafter producing a foaming material by further addingthereto 8.7 kg of a foaming agent (F-1 by tradename produced byDai-Nippon Inki Kagaku Kogyo Corporation), 0.29 kg of a stabilizer(NBA-1 by tradename produced by Dai-Nippon Inki Kagaku KogyoCorporation) and 0.58 kg of a cross linking agent (CATALYST/PA-20 bytradename produced by Dai-Nippon Inki Kagaku Kogyo Corporation), furthermixing in 0.87 kg of a hardening agent (DR-5L by tradename produced byDai-Nippon Inki Kagaku Kogyo Corporation) and 1.45 kg of a thickener(VONCOAT 3750 by tradename produced by Dai-Nippon Inki Kagaku KogyoCorporation), and producing a paint with air bubbles by foaming thismaterial by using a continuous high-pressure foaming machine (TW-70 bytradename produced by Aikosha Seisakusho). This paint was applied on apolyethylene terephthalate (PET) sheet with thickness of 75 μm runningat a rate of 2.0 m/minute by means of a knife coater to a thickness of400 μm. After it was dried in an environment of 100° C., it was furtherdried by far infrared irradiation (120° C. and 140° C.) and cooled bymeans of an ordinary fan for family use to form a foamed layer withdispersed abrading particles on the surface of the PET sheet.

Next, green carbon particles with average diameter of 1 μm weredispersed in a resin solution obtained by dissolving a urethane resinbinder by means of a solvent such as methylethyl ketone to obtain apolishing paint. This polishing paint was applied on the surface of theaforementioned foamed layer by the reverse coating method and then driedto form a polishing layer on the surface of the foamed layer and tothereby produce a cleaning sheet of the test example.

This cleaning sheet of the test example was used to clean the tipportion of a probe by using a wafer prober as shown in FIG. 2 byremoving the semiconductor device which had been inspected therewith andattaching instead the aforementioned cleaning sheet of the test example.The tip portion of the probe was microscopically observed both beforeand after the cleaning process and it was ascertained that the metallicforeign substances found to be attached both at the tip and the sidesurfaces of the probe had been completely removed.

1. A cleaning sheet comprising: a base sheet; a foamed layer formed onsaid base sheet, said foamed layer having non-fibrous abrading particlesdispersed therein; and a polishing layer formed on said foamed layer. 2.A method of producing a cleaning sheet, said method comprising the stepsof: producing a paint having air bubbles dispersed therein bymechanically foaming a foaming material comprising a foaming resinmaterial and non-fibrous abrading particles; forming on a base sheet afoamed layer having abrading particles dispersed therein by coating asurface of said base sheet with said paint and drying said paint; andforming a polishing layer on a surface of said foamed layer.
 3. Themethod of claim 2 wherein the step of producing said paint comprises thestep of sending air into said foaming material while stirring saidfoaming material and thereby dispersing said air bubbles and saidabrading particles inside said paint.
 4. The method of claim 2 whereinthe step of forming said polishing layer comprises the steps of:applying a paint including a resin binder and said abrading particles ona surface of said foamed layer; and drying said applied paint wherebysaid polishing layer is formed on the surface of said formed layerhaving said abrading particles dispersed therein.
 5. A method ofcleaning a probe, said probe having a tip, said method comprising thesteps of: preparing a cleaning sheet comprising a base sheet, a foamedlayer formed on said base sheet, said foamed layer having non-fibrousabrading particles dispersed therein, and a polishing layer formed onsaid foamed layer; causing a surface of said polishing layer to bepressed against said tip of said probe; causing said tip to penetratesaid polishing layer and to be thereby inserted into said foamed layerhaving said abrading particles dispersed therein.
 6. The method of claim5 wherein the step of preparing said cleaning sheet comprises the stepsof: producing a paint having air bubbles dispersed therein bymechanically foaming a foaming material comprising a foaming resinmaterial and abrading particles; forming on a base sheet a foamed layerhaving abrading particles dispersed therein by coating a surface of saidbase sheet with said paint and drying said paint; and forming apolishing layer on a surface of said foamed layer.
 7. The method ofclaim 6 wherein the step of producing said paint comprises the step ofsending air into said foaming material while stirring said foamingmaterial and thereby dispersing said air bubbles and said abradingparticles inside said paint.
 8. The method of claim 6 wherein the stepof forming said polishing layer comprises the steps of: applying a paintincluding a resin binder and said abrading particles on a surface ofsaid foamed layer; and drying said applied paint whereby said polishinglayer is formed on the surface of said formed layer having said abradingparticles dispersed therein.